Low-density iron based alloy for a golf club

ABSTRACT

A low density iron based alloy for making heads of golf clubs, the alloy consisting of essentially 28.0 to 31.5 wt % manganese, 7.8 to 10.0 wt % aluminum, 0.90 to 1.10 wt % carbon and 0.35 to 2.5 wt % titanium, and the balance being iron. Additions of 0.8 to 1.5 wt % silicon and 5.0 to 7.0 wt % chromium are optionally included in the alloy of the invention. Due to the additions of silicon and chromium, the alloy of the invention has an excellent resistance to corrosion. After the alloy has been forged or plastic worked, and then treated under a temperature from 950 degrees Celsius to 1270 degrees Celsius for 1 to 24 hours, an austenitic phase with (Ti, Fe)Cx precipitated in different content rate, the alloy obtains a low density below 6.6 g/cm 3  and distributed within a range of 6.1 to 6.6 g/cm 3 , therefore the alloy with a low density, a high ductility, excellent resistance to corrosion and good finished surface quality is obtained to satisfy requirements of mechanical properties of heads of golf clubs.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an alloy for making heads of golf clubs, particularly to an alloy with low density, high resistance to corrosion and excellent forging surface.

[0003] 2. Description of Related Art

[0004] An alloy is a mixture of metals, such as a metal mixed with additions of metals or sub-metals for various special purposes. When a metal is mixed with other metals or sub-metals, its mechanical properties, such as the melting temperature, strength, ductility, electrical resistance, thermal conductance, heat treatment properties, resistance to corrosion and magnetic properties may be promoted.

[0005] A set of golf clubs generally comprises woods, irons, pitching wedges, sand wedges, putters, etc. The iron club has a shorter striking distance but gives better controllability and a higher striking height than the wood club. In recent years, the iron club has been designed to have a hollow club head in order that the iron club may possess the advantages of the wood club.

[0006] Conventionally, wood clubs are mainly made of wood, particularly persimmon wood. However, due to considering of resistance to corrosion, ductility and high ratio of strength to weight of the golf clubs, raw materials for making the wood clubs are gradually replaced by alloy metals, usually, for example, pure titanium, 6-4 titanium alloy, SP700 titanium alloy, 15-3-3-2 titanium alloy, 2041 titanium alloy, 2205 two-phase stainless steel, 17-4PH stainless steel, AISI431, AISI455, AISI456, aero Al—Li alloy, Be—Cu alloy etc. Wherein pure titanium, 6-4 titanium alloy, SP700 titanium alloy, 15-3-3-2 titanium alloy and 2041 titanium alloy are well known as expensive materials. Presently, these alloy metals are used more popularly than wood in manufacturing of the golf wood clubs.

[0007] Iron clubs are usually made of metals, particularly stainless steels, such as AISI304, 17-4PH stainless steel, AISI431, 2205 two-phase stainless steel, AISI455, AISI456, Be—Cu alloy, soft forging iron etc.

[0008] With reference to the table in FIG. 1, two conventional manufacturing methods of the head of the golf club are listed; one of them is precision lost-wax casting and the other one is forging. Besides the two manufacturing methods listed in the table of FIG. 1, some iron club heads are finished by surface plating, such as nickel-plating, cobalt-plating, etc. and paneling. Of these methods, the method of the precision lost-wax casting has the lower manufacturing cost, however the method of the forging has more advantages than those of the precision casting, which can be seen from a comparison of the table of FIG. 1. A comparison table of mechanical properties between the precision lost-wax casting and the forging is listed in FIG. 2.

[0009] A tendency of designing of the golf club is to increase successful striking with good striking points, and the designing has the following tendencies:

[0010] 1. the heads of the clubs are enlarged in order to increase sweet spots and the probability of successful striking; the volume of the woods can be from 280 cc to 310 cc, and even to 400 cc, and some irons are also formed with some oversized features, particularly such as having a large increased sweet spot.

[0011] 2. the center of gravity of the club head is lowered in order to obtain a very stable striking of the ball, good striking points and long striking distance.

[0012] 3. the shape of the club head is designed to have a strengthened club face with low air drag.

[0013] Additionally, the features of the metal alloys for making the club heads are explained as follows:

[0014] 1. Resistance to corrosion: normally in conformity with the standard of stainless steel 17-4PH harding type in a salt spray test at temperature of 35 degrees Celsius for 48 hours in 5% NaCl.

[0015] 2. Properties of metal alloys for making wood club heads: It normally requires a tensile strength from 1100 to 1500 Mpa, an elongation rate of at least 10%, and it is the higher of the tensile strength and the elongation rate the better of the alloy material for increasing of the bulk and sweet spots of the club head.

[0016] 3. Properties of metal alloys for making iron club heads: The metal alloy for making iron clubs normally requires a tensile strength from 700 to 1000 Mpa, an elongation rate of at least 10%, and it is certainly the higher of the tensile strength and the elongation rate the better of the alloy material for increasing of the bulk and controllability of the club head.

[0017] Additionally, because the standards of the golf club heads are weight,, density and strength of the material are other important facts in designing and manufacture of the golf club. Conventionally, the metal club heads are made from iron based alloys, such as stainless steel or tool steel having their density value from 7.8 to 8.1 g/cm³, or aluminum based alloys, for example harding aluminum having a density from 2.7 to 2.8 g/cm³. These two types of alloys both have their strength ratio (strength/density) lower than 1.8×104. As shown in FIG. 3, mechanical properties and strength of a part of metal alloys are listed in the table.

[0018] Recently, due to development and production of titanium alloy having a density from 4.5 to 4.8 g/cm³ and a strength ratio higher than 2.3×104 m, the manufacturing of the golf club has been changed a lot. However, because the titanium alloy is still very expensive, it is a main object to develop a kind of metal alloy material with low density, high elongation or ductility, and sufficient strength so as to enable the golf clubs to be designed with large bulk, good controllability and stability of striking.

[0019] In the recent one to two decades, it has been found that mechanical properties of Fe—Al—Mn based alloy can be promoted by controlling the contents and by performing heat treatment to obtain high strength and toughness, good resistance of low or high temperature, and resistance to corrosion. The following papers have described these characteristics in detail.

[0020] 1. “Effect of Manganese on the Oxidation of Fe—Mn—Al—C alloys” by C. H. Kao et al., Journal of Materials Science, vol. 23, p. 744, 1988;

[0021] 2. “Phase Decomposition of Rapidly Solidified Fe—Mn—Al—C Austenitic Alloys” by Charles J., et al., Prog., p. 71, 1981;

[0022] 3. “Effect of Potential on the Corrosion Fatigue Crack Growth Rate of Fe—Al—Mn Alloy in 3.5% NaCl Solution” by J. B. Duh, et al., Met. Corrosion, vol. 46, p. 983, 1990;

[0023] 4. “An assessment of Fe—Mn—Al Alloys as Substitutes for Stainless Steels” by J. C. Benz, et al., Journal of Metals, p. 36, 1985;

[0024]5. “Development of Oxidation Resistant Fe—Mn—Al Alloys” by J. Garcia, et al., Met. Progress, p. 47, 1982;

[0025] 6. “Age Hardening of an Fe-30Mn-9Al-0.9C Alloy by Spinodal Decomposition” by Kazunori Sato, et al., Scripta Metallurgica, vol. 22-6, p. 899, 1988;

[0026] 7. “A Further Contribution to the Phase Constitution in (Fe0.65Mn0.35)0.83Al0.17-xC Pseudo-Binary System” by K. H. Han, et al., Scripta Metallurgica, vol. 22, p. 1873, 1998;

[0027] 8. “The microstructures and mechanical properties of an austenitic Nb-bearing Fe—Al—C alloy processed by controlled rolling” by K. H. Han, Materials Science and Engineering, p. 1, 1999;

[0028] 9. “Hot-rolled Alloy Steel Plate” by T. F. Liu, U.S. Pat. No. 4,968,357;

[0029] 10. “The microstructure and stress corrosion cracking behaviour of precipitation hardened Fe-8.7Al-29Mn-1.04C alloy in 20% NaCl solution” by S. C. Tjong, et al., Materials Science and Engineering, p. 203, 1986;

[0030] 11. “Experimental Study of the Phase Equilibria in the Fe—Al—Mn System” by X. J. Liu, et al., Metallurgical Transactions, vol. 27, p. 2429, 1996;

[0031] 12. “Structure and Properties of Austentic Alloys Containing Aluminum and Silicon” by Schmatz, D. J., Trans. ASM, vol. 52, p. 898, 1960;

[0032] 13. “Phase Transformation Kinetics in Steel 9G28Yu9MVB” by Krivonogov, G. S. et al., Phys. Met. & Metal log, vol. 4, p. 29, 1975;

[0033] 14. “An Austenitic Stainless Steel Without Nickel or Chromium” by Banerji, S. K., Met. Prog. P. 59, 1978-4;

[0034] 15. “Phase Decomposition of Rapidly Solidified Fe—Mn—Al—C Austenitic Alloys” by Charles, J. et al., Met. Prog, p. 71, 1981;

[0035] 16. “Development of Oxidation Resistant Fe—Mn—Al Alloys” by Gricia, J. et al., Met. Prog., p. 47, 1982;

[0036] 17. “New Stainless Steel Without Nickel or Chromium for Alloys Applications” by Wang, R. et al., Wet. Prog., p. 72, 1983.

[0037] Overall, the study scope of Fe—Al—Mn based alloy has the following tendency:

[0038] Resistance to corrosion: study results from experts in the world show that when the Fe—Al—Mn alloy contains an aluminum content above 6.5%, surfaces of the alloy form a continuous protective layer (Al2O3),

SUMMARY OF THE INVENTION

[0039] The object of the present invention is to provide a low density iron-based alloy for making a golf club head, the alloy consisting essentially of 28.0 to 31.5 wt % manganese, 7.8 to 10.0 wt % aluminum, 0.90 to 1.10 wt % carbon, and 0.35 to 2.5 wt % titanium, and the balance being iron. Addition elements 0.8 to 1.5 wt % silicon, 5.0 to 7.0 wt % titanium are optionally added to the alloy of the invention. Due to the addition of chromium and silicon, the alloy of the invention has a good resistance to corrosion. After a cast has been cooled down or has undergone a ductile working treatment, and then been treated for 1 to 24 hours under temperature between 950 degrees Celsius to 1270 degrees Celsius, an austenitic iron based alloy is obtained with (Ti, Fe)Cx precipitated with various composition ratios. The density of the alloy material is distributed within a range from 6.1 to 6.6 g/cm³, thereby the alloy material of the invention is obtained with low density and high resistance to corrosion.

[0040] The detailed features of the present invention will be apparent in the detailed description with appropriate reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0041]FIG. 1 is a comparison table showing features of manufacturing methods of the precision lost-wax casting and the forging of heads of golf clubs;

[0042]FIG. 2 is a comparison table showing mechanical properties of conventional alloys for heads of golf clubs;

[0043]FIG. 3 is a comparison table showing mechanical properties of conventional alloys and strength for heads of golf club;

[0044]FIG. 4 is a table of chemical compositions and mechanical properties of the typical Fe—Al—Mn alloys which are published up to present;

[0045]FIG. 5 is a table of chemical compositions of embodiments of alloys in accordance with the invention;

[0046]FIG. 6 is a comparison table showing mechanical properties of the embodiments of the alloys in accordance with the invention;

[0047]FIG. 7 is a chart showing the relationship between the temperature of forging to the surface roughness of the alloy in accordance with the invention;

[0048] FIGS. 8(a, b) are respectively a metallograph and an electromicrograph of an alloy embodiment of the invention after being heat treated for 2 hours at 1100 degrees Celsius;

[0049] FIGS. 9(a, b and c) are schematic graphs showing an amount of (Ti, Fe)Cx being precipitated from the alloys of the invention;

[0050]FIG. 10 is an X-ray actinograph showing distribution of the (Ti, Fe)Cx being precipitated from the alloys of the invention;

[0051]FIG. 11 is a diffraction graph at directions of [0,0,1](a), [−1,1,2](b) and [0,1,1](c) of the (Ti, Fe)Cx being precipitated from the alloys of the invention;

[0052] FIGS. 12(a, b) are respectively an electromicrograph and a diffraction graph of the alloy in accordance with the invention; and

[0053]FIG. 13 is a perspective view of a striking panel of a golf club head made of the alloy of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0054] The present invention relates to a low density iron based alloy for heads of golf clubs, particularly to an alloy having a chemical composition mainly consisting of iron, manganese, aluminum, carbon, titanium, and additionally silicon and chromium.

[0055] The alloy essentially contains 28.0 to 31.5 wt % manganese, 7.8 to 10.0 wt % aluminum, 0.95 to 1.10 wt % carbon, 0.35 to 2.5 wt % titanium, 5.0 to 7.0 wt % chromium, 0.8 to 1.5 wt % silicon, and the balance being iron. As listed in the table of FIG. 5, alloys from code 1 to 10 are practicable embodiments having composition within a range of the present invention, alloys from code 11 to 20 are used for comparison.

[0056] Now with reference to FIG. 6, it is found that an alloy of code 2 has a density of 6.596 g/cm³, a tensile strength reaching 986 Mpa, a yield strength 763.4 Mpa, a ductility of 38.5%, a density of 6.518 g/cm³, and successfully undergoes both a 48-hour 5% salt spray test and a 3000-impact durability test.

[0057] An alloy of code 6 in conformity with material standard of club head has a density of 6.273 g/cm³, a tensile strength reaching 1247.4 Mpa, a yield strength of 895.6 Mpa, a ductility of 10.1%, a density of 6.518 g/cm³, and successfully undergoes both a 48-hour 5% salt spray test and a 3000-impact durability test.

[0058] An alloy of code 11 disclosed by U.S. Pat. No. 4,968,357 has a tensile strength of 1321.4 Mpa, a yield strength of 1242.8 Mpa, a ductility of 36.9, and a density of 6.871 g/cm³.

[0059] An alloy of code 12 disclosed by U.S. Pat. No. 4,968,357 has a tensile strength of 878.5 Mpa, a yield strength of 635.7 Mpa, a ductility of 27.8, and a density of 6.695 g/cm³.

[0060] The alloys of code 11 and code 12 each successfully underwent the 3000-impact test, but failed in the 48-hour 5% salt spray test, and additionally have their density value exceeded by the desired range of the invention.

[0061] It is found that an alloy of code 19 has a tensile strength of 834.5 Mpa, a yield strength of 632.9 Mpa, a ductility of 37.5%, and a density of 6.738 g/cm³, after having been treated for 4 hours at a temperature of 1100 degrees Centigrade. The alloy of code 19 successfully underwent both the 3000-impact test and 48-hour 5% salt spray test, but has a density value exceeded by the desired range of the invention.

[0062] It is also found that an alloy of code 20 has a tensile strength of 821.5 Mpa, a yield strength of 618.9 Mpa, a ductility of 43.5%, and a density of 6.649 g/cm³, after having been treated for 4 hours at a temperature of 1100 degrees Centigrade. The alloy of code 20 successfully underwent both the 3000-impact test and 48-hour 5% salt spray test, but has a density value exceeded by the desired range of the invention.

[0063] Additionally, as shown in FIG. 7, an alloy of code (2) has its surface roughness increased from 2.4 μm to 5.8 μm along with the increasing of the temperature for the hot forging from 900 degrees Celsius to 1200 degrees Celsius. Therefore the alloy for the high quality requirement of heads of clubs must be hot forged below the temperature of 1100 degrees Celsius to obtain a surface roughness below Ra 3 μm.

[0064] In accordance with the present invention, the chemical composition of the alloy should be strictly limited, and the reasons for the limitation are as follow:

[0065] Manganese

[0066] Manganese normally coexists with iron. Since manganese tends to combine with sulfur, the hot brittleness caused by the sulfur can be eliminated. Manganese also helps elimination of oxidates in the alloy. In the high-carbon steel, manganese is combined with carbon to be Mn3C, and with Fe3C to be (Fe, Mn)3C to increase the alloy's strength and hardness. Overall, when the alloy has the manganese content below 23.5 wt %, coarse iron grains are produced in the alloy during the manufacturing, which is not beneficial for the workability and ductility of the alloy. If the alloy contains manganese content above 32 wt %, a large amount of the β—Mn phase is precipitated on the grain boundary, which results in brittleness of the alloy. Consequently the manganese content of the alloy of the present invention is strictly limited to between 28 wt % to 31.5 wt %.

[0067] Aluminum

[0068] Aluminum content has an excellent deoxydation effect, which not only depresses the growing of crystals to disperse the oxidates and nitrides, but is also beneficial to increasing of ductility, workability and toughness of the alloy.

[0069] When the aluminum content in the alloy is larger than 7.3 wt %, the alloy has a good resistance to corrosion. When the aluminum content in the alloy rises above 10.5 wt %, B2 or DO3 phase is precipitated to cause brittleness. Therefore, the aluminum content should be limited within the range of 7.8 wt % to 10.0 wt %.

[0070] Carbon

[0071] In addition to the effect of precipitating carbides, the carbon content works as a strengthening element to enhance the austenite structure. Coarse iron gains are reduced and the austenite structure is stabilized along with the increasing of the carbon content.

[0072] When the carbon content in the alloy exceeds 0.5 wt %, the alloy forms a stable austenite structure. However, due to adjustment of addition of titanium content, the carbon content in the alloy must exceed 0.9 wt %, for example that an alloy of code 17 contains 0.81 wt % carbon content. It is found that the density of the alloy of code 17 is 6.517 g/cm³, which is below the desired value of the invention, and the code 17 failed the salt spray test. Besides, when the alloy contains the carbon content that exceeds 1.3 wt %, carbides are precipitated on the grain boundary so as to be of disadvantage for the elongation of the alloy. Therefore, the carbon content should be limited within the range of 0.90 wt % to 1.10 wt %.

[0073] Chromium

[0074] With the addition of chromium in the alloy, the alloy possesses not only a good resistance to corrosion and oxidation, but also a good hardness and high temperature strength, and particularly has a significant effect on high steel to increase its durability.

[0075] When the chromium content in the alloy is below 5.5 wt %, the heads made from the alloy failed the salt spray test. For example, an alloy of code 20 containing 3.82 wt % chromium content failed the salt spray test. When the chromium content in the alloy exceeds 8.0 wt %, the alloy forms a double-phase containing austenitic iron and coarse iron grains, which reduces the resistance of corrosion of the alloy, therefore the club head made of the alloy failed the salt spray test. For example, an alloy of code 19 containing 8.77 wt % chromium content failed the salt spray test. Therefore, the addition of the chromium should be limited strictly within the range of 5.0 wt % to 7.0 wt %.

[0076] Silicon

[0077] The silicon content added in the alloy eliminates formation of air holes and enhances contractibility and fluidity of the molten alloy steel. However, when the silicon content exceeds 1.5 wt %, the alloy is embrittled. For example an alloy of code 15 containing 2.01 wt % silicon content does not have a sufficient elongation rate. Consequently, the silicon content in the alloy of the invention should be limited within a range of 0.8 wt % to 1.5 wt %, which helps in the casting process of the alloy.

[0078] Titanium

[0079] With addition of titanium content in the alloy, the density of the alloy is reduced and the resistance to corrosion of the alloy is increased. When the titanium content in the alloy is below 0.35 wt %, the effects on density and resistance to corrosion are not appreciable. When the titanium content in the alloy exceeds 2.5 wt %, the elongation rate of the alloy is reduced and is lower than a desired value of 10%. Besides, addition of 0.35 to 2.5 wt % titanium content is beneficial to formation of (Ti, Fe)Cx precipitated phase in different content rates in austenitic based iron, as shown in FIGS. 8 and 9. Wherein the (Ti, Fe)Cx precipitated phase is of advantage to grain refinement. As shown in FIG. 10, this precipitated phase being analyzed under an X-ray energy distribution system (EDS) is a carbide composed of titanium, iron and carbon content, and has a face-centered cube (FCC) structure viewing from an electron microscope, as shown in FIG. 11. Since the based iron contains titanium content of a low content rate or (Ti, Fe)Cx phase precipitated, the density of the metal alloy is lowered to a range of 6.1 to 6.6 g/cm³. According to the results of the invention, the titanium content limited strictly within a range of 0.35 wt % to 2.5 % wt being added in the alloy is beneficial to reducing density and increasing resistance to corrosion.

[0080] Overall, the alloy metal for making golf clubs in accordance with the invention can be hot forged at temperature range of 900° C. to 1100° C., whereby a finished product can have an excellent surface roughness equal or below 3 μm. If the alloy is hot worked at a temperature from 1100° C. to 1200° C., the alloy will have a surface roughness higher than 3 μm in addition to an intensified oxide skin.

[0081] The alloy for heads of golf clubs of the invention has the following advantages:

[0082] 1. Mechanical properties: by controlling contents of aluminum, manganese and carbon, and the additional addition of titanium to refine grain of the alloy material, this alloy as listed in a table of FIG. 8 has a tensile strength range from 921.5 to 1247.4 Mpa, and a yield strength range from 756 to 895.6 Mpa. Club heads made from the alloy after an aging process have a high strength, for example alloys of code 3 and 4, due to the (Fe, Mn)3AlCx carbide integrally precipitated in the iron base, with reference to FIG. 12.

[0083] 2. Low density: due to controlling contents of aluminum, manganese and carbon, and addition of 0.35 wt % 2.5 wt % titanium, the alloy of the invention possesses an austenitic iron based with low rate of titanium and (Ti, Fe)Cx phase precipitated, so that the density of the alloy is lowered to 6.1 to 6.6 g/cm³, and in a same weight standard limitation, the heads made from the alloy of the invention will have a larger volume than the heads made from an alloy with a higher density than that of the alloy of the invention;

[0084] 3. Resistance to corrosion: the alloy of the invention includes additions of 5 wt % to 7 wt % chromium and 0.35 wt % to 2.5 wt % titanium, which is beneficial to increasing resistance to corrosion, and also reduces production cost of the heads of golf clubs.

[0085] Overall, by the controlling composition and the temperature condition of forging, the present invention obtains a low density iron based alloy material for making golf clubs, the alloy particularly has a low density, high strength, and good surface quality of finished products after being forged and tested in the salt spray test.

[0086] It is to be understood, however, that the above illustration is only to clarify the feature of the alloy for making heads of golf club of the present invention, and should not be deemed as the scope of the invention. 

What is claimed is:
 1. A low density iron based alloy for heads of golf clubs, the alloy consisting of essentially by weight 28.0 to 31.5 percent manganese, 7.8 to 10.0 percent aluminum, 0.90 to 1.10 percent carbon, and 0.35 to 2.5 percent titanium, and a balance of the weight of the alloy being iron, the density of the alloy reaching 6.1 to 6.6 g/cm³; and characterized that the alloy of the invention has a surface roughness below 3 μm after having been forged at a temperature within 900 to 1100 degrees Celsius.
 2. The low density iron based alloy for heads of golf clubs as claimed in claim 1, wherein the alloy has added thereto 0.5 to 7.0 weight percent chromium, thereby the resistance to corrosion of the alloy is increased.
 3. The low density iron based alloy for heads of golf clubs as claimed in claim 1, wherein the alloy has added thereto 0.8 to 1.5 weight percent silicon, thereby the ductility of the alloy is increased. 